My Ravenheat rsf100 et Combi Boiler won't ignite?

Please Help? just before i call out a plumber on a sunday, can anyone help??

My boiler Ravenheat RSF 100 ET Combi Boiler, stopped working whilst on yesterday..

The Pilot light comes on, ignition Clicks as though it is going to fire up and then nothing, the pilot light goes out and 15-20 seconds later it tries again..

The bar is 1.25 and the appears to have no visable leaks..

I know thats probably really vague and i have tried Hitting the top right hand corner.. It felt great to take my frustration out.. but alas no CH or HW

Please Help... Hannah